The inductance device comprises a core made of a magnetic material, and a coil for supplying exciting current to the core, the excited core being operated non-linearly along a magnetic hysteresis curve called B-H curve or magnetization curve. The numerical analysis of an electromagnetic field using computers is widely used in the development and designing of inductance devices. However, as devices such as DC-DC converters, etc. have become operated with large current recently, their magnetic circuits have become complicated, for instance, with a large number of magnetic gaps in magnetic paths to alleviate the magnetic saturation of cores. As a result, there is now large discrepancy between the analyzed values and the measured values.
As a method for such numerical analysis, JP 05-099963 A discloses an apparatus for calculating the inductance of a magnetic member excited by alternate current superimposed with direct current, which comprises a first calculation means for calculating a magnetic flux density of the magnetic member for a direct current component, based on the initial magnetization of a magnetic body made of the same material as that of the magnetic member and having a shape of the minimum demagnetization coefficient; a means for determining a material constant from the magnetic flux density calculated by the hfirst calculation means and the incremental permeability of the magnetic material; a second calculation means for calculating a magnetic flux density of the magnetic member for an alternate current component using the material constant; and a means for calculating the inductance of the magnetic member based on the magnetic flux density calculated by the second calculation means. The incremental permeability is calculated from inductance determined by the evaluation of DC superposition characteristics using a ring-shaped sample, the magnetic path length and cross section area of the sample, and the number of coil winding, etc. The magnetic flux density and the incremental permeability are determined from the magnetic field strength of the sample for a superimposed direct current component, and the initial magnetization.
In the inductance-calculating method described in JP 05-099963 A, because the material constant is determined by the evaluation of DC superposition characteristics using the ring-shaped sample, the inductance can be calculated with high accuracy without the trial production of magnetic parts. However, this method is complicated because it needs the evaluation of DC superposition characteristics, and minor loops by alternate current are not considered in obtaining the operating point (magnetic field strength and magnetic flux density) from the DC superposition characteristics and the initial magnetization. Therefore, there is room for further improvement in the accuracy of numerical analysis.
The magnetic properties of inductance devices may change depending on use temperatures, stress, direct current, etc., but JP 05-099963 A does not take such change into consideration. Without considering these factors, the analysis of the magnetic properties of inductance devices is insufficient.